1. Field of the Invention
The present invention relates to the field of geophysical seismic data collection. More particularly, the present invention relates to an integrated system for collecting, storing and processing seismic and navigation data from an exploration prospect, and for enhancing quality control of such data.
2. Background of the Art
Seismic exploration investigates the geophysical structure of formations underlying water. In marine seismic exploration, seismic source arrays are towed by one or more vessels through the water, and sensor arrays detects signals generated by wave reflections from subsurface geologic formations. The seismic source array utilizes air guns or other repeatable sources, and the sensor array typically utilizes hydrophones or other transducers. One or more seismic lines in the same geographic area define a survey, and a collection of one or more related surveys typically define an exploration prospect
As the seismic source array passes over the exploration prospect, the source waves travel downward through the sea floor and the subsurface formations. Portions of the seismic wave energy are reflected back into the water by the sea floor and by interfaces between subsurface rock layers. The returning reflected waves generate pressure pulses, and the sensor array generates output signals representing such pressure pulses. The output signals are recorded on tapes and can be processed to identify certain relationships. For example, the propagation time of a seismic wave from a reflection point is proportional to the depth of the reflection point, and the processed output signals can be merged with position data to generate topographical representations of the subsurface formations.
Marine seismic data acquisition collects vast quantities of seismic and positioning data, and such data represents numerous parameters having multiple error sources. Wind, waves, and currents physically move the seismic streamers relative to the tow vessel in a xe2x80x9cfeathering anglexe2x80x9d relative to the tow vessel heading. A relatively small feathering angle of five percent may offset a streamer point hundreds of meters from the survey line. Errors also occur due to the dispersal of the subsurface wave path reflection points, the occurrence of source and receiver offsets, the inclination of the reflecting surfaces, and because of other factors. The accuracy and usefulness of seismic data requires that multiple data processing procedures accurately locate the data points representing the seismic data.
3-D seismic acquisition on land also generates large quantities of seismic data from a plurality of seismic sources and a plurality of seismic detectors. The acquisition geometry is designed to provide data having high multiplicity of coverage of the subsurface, preferably over a wide range of source-receiver azimuths.
Various data gathering systems collect and process seismic data. In U.S. Pat. No. 4,787,069 to Beauducel et al., electronic modules filtered and amplified signals near each seismic receiver, and an acquisition apparatus digitized, stored and multiplexed signals from the seismic receivers to a ship-based central control and recording device.
U.S. Pat. No. 4,635,237 to Benestad et al. discloses a system for transmitting information between seismic data acquisition devices and a central receiver. Benestad describes how conventional seismic data acquisition systems have multiple electrical contacts and connectors which increase the probability of faults. Arbitrary faults due to an electronic malfunction are identified by a data selector which screens data before the data is entered into the data stream. An extra data transmission line is included for transmitting a data stream following a line break or short-circuit in one of the ordinary transmission lines, and a signal indicating the error is sent to a central control unit.
U.S. Pat. No. 4,561,073 to Aeter et al. discloses a system for sorting seismic data in a marine survey by sorting the data into defined squares, and evaluating the measurement results for each square. By categorizing the data into geographic squares, errors and deviations caused by wind and other conditions are evaluated before the entire data set is processed. If sufficient data for such geographic space is not received, additional seismic data for such geographic space could be acquired.
In U.S. Pat. No. 4,663,743 to Rampuria et al., a data transcriber system receives data in a first medium and outputted the data in a second medium. The transcriber system permits detection and correction of data errors. However, the system requires significant operator intervention to set processing parameters, to choose transcription types and input modes, to view input parameters, to modify data, and to output the data.
In U.S. Pat. No. 4,759,636 to Ahern et al., surrogate seismic signals are produced from multiple selected channels on a real time basis to represent the detected seismic data. These surrogate signals are generated by sampling the multiplexed seismic signal at selected time intervals. The surrogate signals consolidate the data quantities transmitted to a central processor for processing and interpretation. The surrogate signals are further used to evaluate the data quality control and to evaluate and optimize data acquisition parameters.
U.S. Pat. No. 4,682,307 to Newman also seeks to provide a real-time data processing system by reducing the processed data. A single seismic source and a single receiver produce single trace data for processing, thereby reducing the total volume of data processed.
The emergence of 3-D data seismic processing as a geophysical tool and of multiple, large streamer arrays towed behind seismic vessels results in additional data available for processing. Known processing systems that selectively sampled the data sets ignore much of the available data.
U.S. Pat. No. 5,920,828 to Norris et al. teaches an automated quality control system for collecting seismic data from a seismic acquisition system, and for processing data from a marine navigation system. The invention includes a seismic data storage engaged with the seismic acquisition system for receiving and storing seismic data, a seismic data processor engaged with the seismic data storage for processing seismic data, a prospect data logger for accessing the positioning data and for coordinating seismic data processing and for identifying and storing attributes and data, and a terminal communicating with the prospect data logger for permitting commands to be transmitted to the prospect data logger.
However, even with the most sophisticated systems, quality control (QC) of the acquisition of the vast amount of data present in a typical 3-D seismic acquisition remains problematic. In particular, present systems do not take into account patterns of disturbances in a typical 3-D seismic data volume caused by common sources of errors and noise. There is a need for a display system that makes visualization of these disturbances in a 3-D data acquisition easier. The present invention satisfies this need.
The present invention is a method for displaying, attributes of the quality of seismic data in seismic data acquisition and processing. The data may have been acquired in a receiver-based acquisition geometry (e.g., from single-component or multi-component ocean-bottom cables) or from a shot-based acquisition geometry (e.g., from towed sources and receivers). In one embodiment of the invention, the attributes of the quality of the seismic data are displayed in a hypercube with the coordinate axes related to the acquisition geometry. In an alternate embodiment of the invention, three mutually orthogonal axes are defined to describe the relative positions of each pre-stack trace of seismic data. Using visualization methods that have been developed to display attributes of seismic data indicative of subsurface geology, the present invention displays attributes indicative of the quality of the seismic data itself. In the 3-D display, certain kinds of disturbances that affect the quality of the seismic data have associated patterns in the 3-D volume that make diagnosis of problems in the data acquisition easier.